1. Field of the Invention
The present invention relates to communication networks, and more particularly, to bandwidth allocation in a network with distributed control.
2. Description of the Related Art
Radio Local Area Networks (LAN) typically cover an area of technology where the computer industry and the wireless communications industry merge. Conventional computer networking has relied on wired LANS, typically packet-switched and targeted for data transfer. By contrast, wireless networking, and in particular cellular networking, has relied on wide area networks, typically circuit-switched and targeted for voice transfer. Most efforts in the design of radio LANs have reused the principles that are used in wired LANS. This, however, is a questionable procedure because the environments of the wired medium and of the wireless medium differ in important ways. Moreover, multimedia communications require additional features due to the special traffic characteristics posed by data, voice and video. Finally, the residential environment has its own requirements, which can be decisive for the design of the system.
Almost 100 percent of the computer networks today use a wired infrastructure. The wired medium can range from a simple twisted pair to an optical fiber. Due to its shielded and controllable environment, low interference levels and stable propagation conditions characterize the wired medium. Consequently, the wired medium has potential for high to very high data rates. Because of the latter, all participants in wired LANs typically share this single medium. The medium constitutes a single channel, which is used by only a single one of a number of different users at any given time. Time-division multiplexing (TDM) is used to allow different users to access the channel at different times. The protocols for accessing wired media have been standardized by the IEEE in its 802 series. Typically, multiple access reservation techniques like carrier-sensing (e.g., Ethernet, 802.3 Carrier-Sense Multiple Access/Collision Detect (CSMA/CD) or tokens (e.g., 802.4 token buses, or 802.5 token rings) are used to gain access to the medium. These protocols can be used in a distributed sense in that the user occupying the channel reserves the medium by its present transmission or by its token.
In these schemes, every user can hear all traffic. That is, in a single LAN, all users share not only the channel, but also all of the information carried on that channel. When the number of participants grows, the LAN can be divided into smaller LANs or segments, which channels operate independently. LANs can be interconnected via bridges or routers, which form interfaces between the different local networks. These configurations result in more complex networks. For example, reference is made to D. Bertsekas and R. Callager, Data Networks, 2nd Edition, Prentice-Hall, London, 1992, which is hereby incorporated herein by reference.
For the discussion of the residential LANS, it suffices to consider the single LAN. The LAN typically provides a connectionless packet-switched service. Each packet has a destination address (and usually a source address as well) so that each user can determine whether the packet that passes by is intended for him or not. It will be understood that the net throughput per user in a single LAN is determined by the peak data rate on the channel and by the number of users that share this channel. Even if the peak data rate is very high due to the wide bandwidth of the wireline medium, the effective user throughput can be low if the channel has to be shared among many users.
Since types of communication that take place over current wired LANs are asynchronous and connectionless, current LANs are ill suited for supporting delay-critical services like voice. Voice services demand synchronous or isochronous connections, which require priority techniques in the Medium Access Control (MAC) protocols in order to give voice users precedence over non voice users. If priority services are involved, usually a centralized control scheme is used. In these schemes, a centralized unit (e.g., a base station) controls all traffic on the channel. It instantaneously allocates bandwidth for each user and can therefore prioritize delay-sensitive traffic like voice or video. However, using centralized control is less attractive for networking because the network communication units preferably are peers to one another. For example, the worldwide Internet is based on a peer-to-peer protocol. In these protocols, the channel is the key element of the network. Communication units that are added to the network may gain access to the channel by distributing the channel access control. However, the concept of distributed control and the peer concept goes against the usage of priority traffic in which certain communication units (providing delay-sensitive traffic) should have priority over other communication units. With the advent of multimedia services, prioritization has become essential.
Recently, a different distributed protocol was proposed that is based on a Ping-Pong protocol that involves a virtual token distribution. This is described in “Method and apparatus for medium access on a radio channel” by J. C. Haartsen, U.S. patent application Ser. No. 60/180,095, filed Feb. 3, 2000, which is hereby incorporated herein by reference in its entirety. In accordance with this scheme, each packet transmission coincides with a token exchange. Communication unit A, owning the token, can send a packet to communication unit B. Communication unit B, receiving the packet, also receives the token and is therefore allowed to transmit as soon as the packet from communication unit A has been received. To allow for prioritized traffic, priority or recovery slots are defined, which give a communication unit unconditional access to the channel. For example, when a priority slot associated with communication unit A arrives, communication unit A is allowed to transmit regardless of whether it received the token by means of a previous packet transmission; that is, at a priority slot, the token is given unconditionally to the communication unit associated with the priority slot.
The token Ping-Pong protocol as described in U.S. patent application Ser. No. 60/180,095 does not describe how the token is distributed among the communication units in the interval in between the priority slots. A communication unit that receives the token can send the token (along with its transmission) to any unit, but there are no rules governing to which communication unit the token should be sent. Therefore, when two communication units exchange information continuously, they keep exchanging the token between themselves while other communication units are starved (apart from the communication units that have priority slots that receive the token unconditionally some of the time). Yet, if a token distribution strategy is to be considered, the bandwidth requirements of the participants should be taken into account. Thus, there is a need in the art for a token distribution scheme that enables the token to circulate between the communication units participating on the channel, while at the same time taking into account the bandwidth requirements of the participants.